1. Field of the Invention
The present invention relates to a motor that electronically alters current paths by using plural transistors.
2. Description of the Related Art
In recent years, many office automation apparatus and audio visual apparatus use motors that electronically alters current paths by using plural transistors. For example, there is a motor that alters current paths to windings by using both PNP-type power transistors and NPN-type power transistors.
FIG. 34 shows such a prior art motor, the operation of which will be described. A rotor 2011 has a field part formed by a permanent magnet. According to the rotation of the rotor 2011, a position detecting block 2041 generates two pairs of three-phase voltage signals K1, K2, K3 and K4, K5, K6. A first distributing block 2042 generates three-phase lower conduction control signals L1, L2, and L3 corresponding to the voltage signals K1, K2, and K3, and controls the conduction of lower NPN-type power transistors 2021, 2022, and 2023. A second distributing block 2043 generates three-phase upper conduction control signals M1, M2, and M3 corresponding to the voltage signals K4, K5, and K6, and controls the conduction of upper PNP-type power transistors 2025, 2026, and 2027. Consequently, three-phase drive voltages are supplied to three-phase windings 2012, 2013, and 2014.
This prior art motor, however, has the following various problems.
(1) Large Power Loss
In the prior art configuration, the emitter-collector voltages of the NPN-type power transistors 2021, 2022, and 2023 and the PNP-type power transistors 2025, 2026, and 2027 are controlled in analogue fashion, thereby supplying drive currents of necessary amplitude to the windings 2012, 2013, and 2014. Consequently, the residual voltage drop across the power transistor in activated period becomes large, and the product of this residual voltage drop and the conducted current of the power transistor causes a large power loss. Especially, since the drive currents to the motor windings are large, the power loss has been extremely large. As a result, the motor has a very low power efficiency.
(2) Expensive Cost
In order to reduce the manufacturing cost of a motor, it is very effective to integrate transistors, resistors, and the like onto a single chip as an IC. However, a large chip area is required to compose those PNP-type power transistors 2025, 2026, and 2027, thereby increasing the cost. In addition, when those transistors and resistors are integrated on an IC chip, it is also difficult to carry out a fast operation of PNP-type power transistors due to the effects of parasitic capacitances. Moreover, power loss and heat generation of the power transistors are also too large to integrate them into an IC. Especially, since the drive currents to motor windings are large, the IC is likely confronted with a thermal breakdown caused by the heat generation from those power transistors. If a radiating plate is provided to the IC in order to prevent such a thermal breakdown, the cost is then increased greatly.
(3) Large Motor Vibration
In recent years, in optical disk apparatus such as DVD-ROM and magnetic disk apparatus such as HDD and FDD, a motor with reduced vibration is strongly demanded because of higher density recording and/or playing back on/from such disks. In the prior art configuration, however, when a power transistor is changed over abruptly, a spike voltage is generated in a winding, thereby pulsating the drive currents. Consequently, the generated force of the motor is pulsated and a large motor vibration occurs.
It has been strongly desired to develop a motor in which each of or all of these problems are solved.
It is therefore an object of the present invention to solve the above problems, respectively or concurrently and provide a motor that has the configuration suitable for implementation in integrated circuit form.